Geo-engineering is the study and implementation of technical ways to change (and arguably improve) things like weather patterns, river paths, soils, climates and sea currents on Earth. Recently, geo-engineering has received special attention for efforts to combat global warming.

Direct air capture of carbon dioxide is a method that takes carbon dioxide out of ambient air, as opposed to carbon dioxide that is captured from the point of emissions, say, from the smokestack of a coal-fired power plant.

Lackner and his team are developing a device they call an air extractor, modeled after what is most abundant in nature: the leaf of a tree. There is about 0.5 liter of carbon dioxide in a cubic meter of atmosphere. When the extractor is dry, it loads itself with carbon dioxide from the air; when it's wet it releases carbon dioxide it has captured.

“We can do this at a cost of about $30 a ton of carbon dioxide”, says Lackner, “we have designed a box that can extract about a ton of carbon dioxide a day; it fits into a shipping container”. “If we had 100 million of them", Lackner adds, “we could extract more carbon dioxide out of the air then is currently put in.”

The carbon can be stored in the form of mineral carbonate rock or it can be injected deep in the ground. Alternatively, the carbon dioxide can be used, e.g. by turning it into a fuel. Airplanes will likely need to be powered by fuel for a long time, so captured carbon dioxide could be used to more sustainably produce synthetic jetfuel.

In his lab at Columbia's Engineering School, Lackner has built a small greenhouse, demonstrating that air extractors loaded with captured carbon dioxide can be placed inside a greenhouse; the humid atmosphere inside the greenhouse will make that the carbon dioxide is released. Adding carbon dioxide to the air inside greenhouses is beneficial for plant growth; the plants will take the carbon dioxide out of the air and use it to grow.